From the Americas to Southeast Asia: Navigating The Genomic Waves of Fall Armyworm () Invasions.

The fall armyworm (FAW), scientifically known as , is an agricultural pest native to the American continents. Its larvae display voracious feeding behavior with a host range of over 350 plant species. The pest was first detected outside the Americas in 2016, subsequently spreading across Africa, Asia, and Oceania. As a country with substantial agricultural imports and exposure to regional migration routes, Malaysia presents a valuable case study for investigating the establishment and adaptation of invasive FAW populations. Forty-two novel Malaysian FAW genomes were sequenced on the DNBSEQ-G400 platform via DNBSeq. A subset of high-quality genome-wide single nucleotide polymorphisms was used to compare the evolution of both native and invasive FAW populations, with publicly available samples from another 18 countries from across the world. Our analyses revealed clear genetic differentiation between native and invasive FAW populations. We found little evidence to support West African populations as the founding source for Asian or East African invasions. Instead, Malaysian FAW clustered closely with populations from India, China, and East African countries, suggesting multiple, independent introductions into the region. Genomic outliers related to sensory perception, insecticide resistance, and heat tolerance were detected, likely contributing to the recent global success of FAW invasions. This study provides new genomic insights into the invasion history and adaptive strategies of FAW in Malaysia, contributing to a clearer picture of FAW movement across Asia and Africa. The results provide critical information for future pest management and policy-making to mitigate the spread of this invasive pest.